European soot suspected in mid-1800s retreat of alps glaciers

A study of the abrupt retreat of mountain glaciers in the European Alps in the 1860s has uncovered strong evidence that absorption of sunlight in snow by soot, or black carbon, released by a rapidly industrializing Europe was to blame.

The study, led by NASA and co-authored by a researcher at UC Davis, and is being published today, Sept. 3, in the journal Proceedings of the National Academy of Sciences.

The research may help to resolve a longstanding scientific debate over when the "Little Ice Age" actually ended and why the Alps' glaciers retreated decades before global temperatures started increasing again. The Little Ice Age was a cooling period roughly between the 16th and 19th centuries, though scientists do not agree on when it specifically began and ended.

"We think we've solved the puzzle of why the glaciers in the Alps retreated so quickly," said Richard A. (Tony) VanCuren, an air particles expert with the UC Davis Air Quality Research Center.

The results show that human influence on glaciers reaches back to well before industrial temperature increases.

"Before now, most scientists have believed the end of the Little Ice Age in the 1800s was due to a natural climatic shift, distinct and well before emissions of carbon dioxide reached levels that could start to influence climate and glaciers in the 20th century," said lead author Thomas Painter, a snow and ice scientist at NASA's Jet Propulsion Laboratory in Pasadena.

Glacier records in the European Alps date back to the 1500s, while records of weather conditions date back to the late 1700s. Between 1860 and 1930, large valley glaciers in the Alps abruptly retreated an average of nearly 0.6 mile while temperatures in Europe dropped nearly 1.8 degrees Fahrenheit. Glaciologists and climatologists have been challenged in reconciling this apparent conflict between the climate and glacier records.

To help scientists understand what was driving the glacier retreat, the scientists turned to history.

In the decades following the 1850s, Europe was undergoing a powerful economic and atmospheric transformation, spurred by industrialization. Residents, transportation, and, perhaps most importantly, industry in Western Europe began burning coal in earnest, spewing huge quantities of black carbon and other dark particles into the atmosphere.

For this study, VanCuren analyzed air pollution data from the coal, steel and rail industries in Europe going back to the late 19th century to help determine when and where pollutants were deposited in the glaciers.

Black carbon particles are the strongest absorber of sunlight by weight. When these particles settle on snow, they darken the surface and cause it to melt faster, revealing glacier ice earlier in the year.